Depression need not linger if a new class of drugs that can improve symptoms within hours becomes available. People with depression are often treated with drugs that increase levels of serotonin and other mood-enhancing chemicals in the brain. But these drugs typically take weeks, or even months, to work. Drugs that target receptors for a chemical called NMDA appear to take effect much faster. Ketamine is one example. It can reduce symptoms of depression within hours, but also has hallucinatory side effects.